How to detect when a css3 transition is over

Question

I am learning about javascript and css3 games and I am working on an alien game. The game is a guessing game where you enter a guess of X and Y position and the missile moves towards the alien using css3 transition. When the missle reaches the alien the explosion is supposed to appear; but I am having difficulty detecting when the transition is over. Currently the explosion appears right when you make the X and Y guess and the missle takes off. How can I detect with Javascript when the css3 transition is over to make the explosion appear?

Here is what I currently have:

the stylesheet:

#explosion
{
  width: 20px;
  height: 20px;
  position: absolute;
  display: none;
  background-image: url(../images/explosion.jpg);
}

#alien
{
  width: 20px;
  height: 20px;
  position: absolute;
  top: 20px;
  left: 80px;
  background-image: url(../images/alien.jpg);
}

#missile
{
  width: 10px;
  height: 10px;
  position: absolute;
  top: 240px;
  left: 145px;
  background-image: url(../images/missile.jpg);
  /*Transition*/
  -webkit-transition: all 0.5s ease-out 0s;
  -moz-transition: all 0.5s ease-out 0s;
  transition: all 0.5s ease-out 0s;
}

And the Javascript:

if(guessX >= alienX && guessX <= alienX + 20)
{
  //Yes, it's within the X range, so now let's
  //check the Y range
  if(guessY >= alienY && guessY <= alienY + 20)
  {
    //It's in both the X and Y range, so it's a hit!
    gameWon = true;
//move missle towards alien

//make explosion appear
explosion.style.top = alienY + "px";
explosion.style.left = alienX + "px";
explosion.style.display = "block";

  endGame();
 }
}

Answer 1

I use the following, found here: https://stackoverflow.com/a/13862291/2312574

$('div').on('transitionend webkitTransitionEnd oTransitionEnd otransitionend MSTransitionEnd', function() { 
    // do something
});

Answer 2

Use transitionend event to detect when transition is finished.